This invention pertains to acoustic baffles provided between adjacent rows of tubes in tubular type heat exchangers. It pertains particularly to flexible corrugated-shaped baffles located between adjacent staggered rows of tubes in a tube bank to prevent flow induced acoustic vibrations in a tubular heat exchanger.
Flow channels of heat exchangers or steam generators containing tube arrays can be subject to acoustical resonance vibrations excited by flow of air, gas, or steam transversely across the tubes. Such resonance occurs when the frequency of a flow periodicity inside the tube bank coincides with an acoustical (standing wave) mode of the flow channel. The acoustical modes primarily excited are those which are related to the dimension perpendicular to both the fluid flow direction and the tubes axes. At resonance, an intense sound can be generated which is typically sufficient to cause noise and vibration problems within the heat exchanger.
The elimination of such resonant condition and vibration may be achieved by suppression of the excited acoustic (standing wave) modes. The commonly used method of suppressing standing waves is by use of acoustic baffles. Typically, plate baffles are placed within the tube bank parallel with the flow direction. These baffles divide the flow chamber into separate flow channels, each having a higher natural acoustic frequency than the natural frequency of the unbaffled chamber. The number of baffles used and their location within the width of the flow channel will depend on the acoustical mode frequencies which need to be achieved in order to prevent resonances.
In tubular heat exchangers having a staggered tube arrangement, there is ordinarily no room to place a baffle in the direction parallel with the flow. The only way a baffle could be inserted into the staggered tube bundle would be if space for a baffle was made by eliminating a number of tubes in alignment. However, such a solution represents a great complication in construction in that it affects the uniformity of the tube bundle and reduces the total heat transfer surface. Also for a retrofitting arrangement in heat exchangers for which acoustic baffles have to be inserted to eliminate noise in an operating unit, a structural modification involving tube removal would be prohibitively expensive.
The general use of baffles in tubular heat exchangers is known. For example, U.S. Pat. No. 1,711,622 to Vennum discloses a baffle arrangement used for water tube steam boilers in which a bank of vertically extending tubes have a plurality of straight baffles which extend at an angle through spaces between some of the rearward tubes, so as to protect those tubes from direct contact with the hot furnace gases. U.S.Pat. No. 2,655,346 to Corbitt et al discloses a heat exchanger having a matrix of parallel tubes carrying a first fluid, and having flat baffles arranged in various configurations to control transverse flow of a second fluid past the tubes. Such baffles are spaced apart so as to control fluid flow generally transverse to the tubes, but they do not support the tubes.
U.S. Pat. No. 3,163,208 to Cuzzone et al discloses use of transverse braces for supporting and inhibiting vibration of elongated finned tubes used in heat exchangers; but corrugated shaped baffles are not utilized. U.S. Pat. No. 3,720,259 to Fritz et al discloses a heat exchanger having spirally wound tubes which are supported by a spacer structure. The spiral tubes are separated into groups by a series of conical-shaped straight baffles which are oriented upwardly and provide flow passages generally transverse to the tube bundle. The tubes are each supported by upwardly extending curved wires each having a wave-shaped configuration.
U.S. Pat. No. 4,204,570 to Eisinger discloses helical-shaped tube spacers placed between adjacent tubes in a heat exchanger to support the tubes, but the spacers do not provide any useful baffling function for fluids passing transversely through the heat exchanger. U.S. Pat. No. 4,662,434 to Porowski discloses use of straight vibration dampening spacer tubes which extend transversely between adjacent tubes in a heat exchanger to laterally support the tubes, but the spacer tubes provide no significant acoustic baffling function for fluids flowing external to the heat exchanger tubes.
U.S. Pat. No. 4,796,695 to Cannon discloses a tubular heat exchanger having parallel tubes supported by corrugated slats positioned in empty lanes to separate adjacent rows of tubes. The corrugations extend along the length of the slat to support the tube and generate turbulence in transverse flow of gas, and are made of resilient material such as spring steel so as to press against the adjacent rows of tubes.
Although the prior art has disclosed various types of baffles for use in tubular heat exchangers, it has apparently not provided flexible acoustic baffles which are corrugated in shape and which can be inserted into staggered tube banks of heat exchangers to eliminate resonant flow conditions and acoustic vibrations in the heat exchangers.